COMPARATIVE SURFACE STUDIES ON FINE-GRAIN AND SINGLE

As the surface magnetic field in niobium cavities ap-proaches the theoretical critical field, RF losses grow sen-sitive to increasingly subtle features of the material and the surface. A striking example is the familiar onset of the high field Q-slope, where RF losses increase exponentially with field. A surprising feature of the high field Q-slope is its positive response to a mild baking at 100-120◦C. But the Q-slope returns after the first 20 nm of the niobium metal surface is converted to loss-less pentoxide via anodization. The latter result suggests that the cause of the fast growing losses resides in the first 20 nm of the RF surface. Al-though there are several propositions, the exact mechanism for the high field Q-slope is not yet fully understood and demands further research. We are conducting surface ana-lytic studies with optical profilometry, EBSD, XPS, Auger and SIMS to shed light on the mechanism of the high field Q-slope. We are comparing the behavior of fine-grain nio-bium with single crystal niobium, buffered chemical pol-ishing (BCP) treatments with electropolishing (EP) treat-ments and properties before and after 110◦C bake. Our approach is based on identifying lossy regions, dissecting of these regions and range of analysis